U.K. submarine joins search for missing plane

SYDNEY--A U.K. submarine has joined the search for Malaysia Airlines Flight 370 in the southern Indian Ocean, a sign that authorities are gearing up to scour the seabed for the "black-box" flight recorders even though no plane debris has been found.

The deployment of HMS Tireless bolsters a multinational search for the missing Boeing 777-200 that has so far relied on a combination of satellite and radar data to look for wreckage floating in an area of sea the size of Arizona. Nine military aircraft and an equal number of ships are due to search an area of sea around 1,500 kilometers (932 miles) northwest of the Western Australian capital of Perth on Wednesday.

Australian authorities say the area remains their best bet for finding the plane, but haven't ruled out the possibility that they are looking in the wrong place. They calculate there might be less than a week left before Flight 370's black-box flight recorders stop emitting signals that could help searchers locate them deep underwater.

With time running out, authorities are calling for more help. The U.K. Ministry of Defence is sending HMS Echo, a military survey vessel that can map the depths of the ocean, to the search zone. Malaysian Defense Minister Hishammuddin Hussein said earlier this week that he would ask his counterparts from the U.S. and the Association of Southeast Asian Nations for high-tech equipment that can search deep below the ocean's surface.

An Australian vessel carrying a U.S. Navy black-box locator that can detect flight-recorder signals left from Perth for the search area Monday night after completing trials. Ocean Shield, a vessel built to operate in Antarctic weather, is expected to arrive in the search area by April 5--leaving teams as little as two days to locate the recorders in depths of some 2,000 to 4,000 meters (6,500 to 13,000 feet).

The beefed-up search effort comes as Malaysian Prime Minister Najib Razak was set to visit Perth on Wednesday and Thursday in a show of support for the operation, which has already drawn in aircrews from China, Japan, South Korea and New Zealand as well as several commercial and military ships.

Malaysia's police chief Wednesday tried to lower expectations of a quick and conclusive determination of what caused the disappearance of Flight 370, but asked for patience as investigators question more people.

"Give us more time," Inspector General of Police Khalid Abu Bakar told reporters. "We may not even know the real cause of this incident."

Malaysian investigators believe Flight 370 crashed in the southern Indian Ocean when it ran out of fuel, thousands of kilometers from the nearest airport, after disappearing from civilian radar on March 8. All of the 239 passengers and crew are assumed dead.

On Tuesday, Mr. Hishammuddin reiterated Malaysian investigators' belief that the way Flight 370 flew before it disappeared from radar was consistent with "deliberate action" by someone on the plane.

Still, radio transmissions from the last contact the plane had with air-traffic controllers show nothing unusual in the minutes before it disappeared from radar, according to a transcript.

Australian authorities abruptly shifted the search zone in the southern Indian Ocean some 1,100 kilometers (680 miles) to the northeast last week, to about 1,850 kilometers west of Perth, based on new calculations of the radar data. Wednesday's search overlaps part of the area already inspected by military aircrews.

"We are working from a very uncertain starting point," Air Chief Marshal Angus Houston said in the first briefing since his Joint Agency Coordination Centre took responsibility for providing regular updates on the search Tuesday.

"We don't know what altitude the aircraft was traveling at. We don't really know what speed it was going at other than some information that gives us some idea of the speed. It is a very inexact science," the former chief of Australia's defense force said.

Now in its fourth week, the search for Flight 370 has yielded little except satellite images and aerial photographs of objects that haven't been linked to the missing plane. Numerous ships engaged in the hunt have hauled in only unrelated scraps of junk in an area where currents frequently bring together floating garbage.

Wing Commander Andy Scott, of the Royal New Zealand Air Force, said hopes raised by the sighting of two interesting objects among 14 bits of debris in the ocean Monday were dashed later when the objects turned out to be garbage.

"As much as you want to try and find some signs of Flight 370, it's also almost equally important to find nothing so you can discount the area," Wing Commander Scott said. "You can put your hand on your heart and say, "Well, there's nothing there." That means we can then move on to another area."

Authorities cite the example of an Air FranceAirbus A330 that plunged into the Atlantic Ocean in 2009. It took investigators almost two years to retrieve the plane's flight recorders, even though the plane was traveling on a well-established flight path when it crashed and searchers retrieved some aircraft debris within days.

Rebecca Howard in Wellington and Jason Ng in Kuala Lumpur contributed to this article.

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